1. Field
The described technology generally relates to a device for electro-optical sampling of a microwave frequency signal comprising a microwave transmission line for transmitting a microwave signal.
2. Description of the Related Art
The described technology is applicable in the field of electro-optical sampling of microwave signals, whereof the frequency band is in the range from several gigahertz (GHz) to several hundred GHz. A number of applications in the field of radar and telecommunications make use of such microwave signals.
It is a known technique to use for the sampling of microwave signals, carried by an interrupted microwave line, an interrupter switch controlled by a reference optical signal, or ultrafast optical “gate”, which switches between an “open” state and a “closed” state at very specific time instants, in a cyclical timed manner, in order to sample the microwave electric signal. A mode-locked laser is used for the generation of the optical control signal in order to reduce the timing jitter. Such an optical signal controlled interrupter switch must have a fast response time, of the order of a picosecond.
At the present time there are known optically controlled interrupter switches manufactured out of epitaxial gallium arsenide (GaAs) semiconductor material at low temperature, which has an electronic band gap of 1.43 eV (electron volts). This semiconductor is rendered conducting by an optical signal of high power, having a wavelength of 0.8 μm. A mode-locked laser transmitting at 0.8 μm is relatively expensive, and in addition, a very high peak power is necessary for the switch to be effective.
A number of studies have focused on the development of an optically controlled interrupter switch that is sensitive to the wavelength of 1.5 μm, which takes advantage of less expensive components such as lasers and uses know-how developed in the field of telecommunications. In particular, the use of semiconductor material having lower electronic band gap has been studied.
However, the time for recombination of the carriers generated in such semiconductors is generally not sufficient for satisfying the constraint of a switching time of the order of a picosecond or indeed comes at the cost of degraded performance such as a significant dark current.
It is desirable to overcome the drawbacks of existing systems by offering an optically controlled interrupter switch for microwave line that is more efficient, and thus which requires a control signal of somewhat lower power, while having a switching time of the order of a picosecond.